Threats at the client side

• Application data at rest: With the introduction of mobile applications, the concept of storing data at the client side has been drastically adopted. Many mobile applications store sensitive data on the device without any encryption. This is one of the major problems of mobile applications. This data can be sensitive, confidential, and private. Data that rests on the device can be exploited in many different ways. An attacker who has got physical access to the device can gain access to this data almost without doing anything. A malicious application may gain access to this data if the device is rooted/jailbroken. It is important to make sure that apps do not store sensitive data such as usernames, passwords, authentication tokens, credit card numbers, and so on, on the device. If it cannot be avoided, it is required to encrypt it and keep it away from an attacker's control. We will explore more details about insecure data storage vulnerabilities in Chapter 5, Data Storage and Its Security.
• Application data in transit: Mobile applications that communicate with the backend are highly exposed to attacks that target the data in transit. It is quite common for end users to join publicly available networks at coffee shops and airports where an attacker may sit in and eavesdrop on the data using tools like burp proxy, MITM proxy, SSL MitM (short for Man in the Middle attack) proxy, and so on. With the introduction of smart phone apps, exploitability of such attacks became very easy as mobiles follow us wherever we go.
• Vulnerabilities in code: Mobile applications when developed with no security controls in mind can become vulnerable to various attacks. These coding mistakes in the app can lead to a serious vulnerability in the app, which in turn impacts the user/app data. Examples of such mistakes include, exported content providers, exported activities, client side injection, and so on. Attack scenarios include, an attacker who has physical access to the device may gain access to another user's session. A malicious app sitting on the same device can read the content of the other apps when they expose data due to coding mistakes. An attacker who has access to the binary may decompile the application and view the hardcoded credentials in the source code.
• Data leaks in the app: This is another issue in mobile applications in almost all the platforms. It is possible that an app may unintentionally leak sensitive data to an attacker. This requires extra attention from the developer. The code he uses for logging during the development phase must be removed and he must make sure that no data is prone to leaks. The main reason behind focusing on this is that application sandboxing will not be applicable to some of the attacks in this class. If a user copies some sensitive data such as a security answer from an application, this will be placed on the device clipboard, which is out of the application sandbox. Any other app sitting on the same device can read this data copied without the knowledge of the first app.
• Platform specific issues: When designing a threat model for mobile applications, it is important to consider the threats associated with the platform that this app is going to run on. Let us consider an example with Android, native apps that are developed for the android platform can be easily reverse engineered and the Java source code can be easily viewed. It allows an attacker to view the source code as well as any sensitive data that is hard coded in the code. It is also possible to modify the code in the application and re-compile it and then distribute the apps in third party markets. Performing integrity checks is something that has to be considered if the app is sensitive in nature or if it is a paid app. Though the above-mentioned issues are relatively less effective in a platform like iOS, it has got its own platform specific issues if the device is jail-broken.